Carbon-13 Magnetic Resonance: the Stereochemistry of 1,2- and 1,3-Dimethyl-4-phenylpiperidine Derivatives

Abstract

The carbon-13 magnetic resonance spectra of the diastereoisomers of 1,2-dimethyl- (1) and 1,3-dimethyl-4-phenylpiperidin-4-ol (2), their esters and corresponding hydrochlorides have been determined. The observed chemical shifts can be ascribed to charge polarization or steric effects. The latter is particularly important in establishing the axial configuration of the 4-phenyl group and 3-methyl group in the preferred conformations of α-1 and β-2, respectively, and consequently the stereochemistry of these systems. Substituent additivity effects are similar to those in the piperidones and cyclohexanes. Solvent effects on 13C resonances remove the ambiguities of conformational change suggested in earlier proton studies.